Heterostructured TiO₂ Nanoparticles/Nanotube Arrays: In Situ Formation from Amorphous TiO₂ Nanotube Arrays in Water and Enhanced Photocatalytic Activity

Abstract Heterostructured TiO 2 nanoparticles/nanotube arrays (NPs/NTAs) are produced from as‐anodized amorphous TiO 2 nanotube arrays in water at a temperature as low as 90 °C. The phase and morphology transformation of the as‐anodized amorphous TiO 2 nanotube in water can be attributed to a water‐induced dissolution and recrystallization mechanism in which the as‐anodized amorphous TiO 2 NTAs are gradually self‐sacrificed, and then spontaneously morphing into the composite NPs/NTAs structure consisting of anatase NPs and thinner amorphous NTs. The composite can be further crystallized into anatase TiO 2 NPs/NTAs consisting of anatase NT and anatase NPs by annealing in air at 450 °C for 3 hours. The composite anatase TiO 2 NPs/NTAs have a surface area that is 1.4 times larger than that of the anatase TiO 2 NTAs and possess enhanced photocatalytic activity in the photodecomposition of organic pollutants and water splitting. The photodecomposition rate of the organic pollutant rhodamine B by the anatase TiO 2 NPs/NTAs photocatalyst is two times higher than that by the annealed anatase TiO 2 NTAs. The enhanced photocatalytic activity of the hererostructured TiO 2 NPs/NTAs arises from the large surface area of the TiO 2 NPs and superior electron transport in anatase TiO 2 NT. The in situ hydrothermal conversion of the microstructure from amorphous TiO 2 NTAs into hererostructured TiO 2 NPs/NTAs in water is very simple thereby enabling the design and fabrication of highly photoactive one‐dimensional TiO 2 ‐based functional materials applicable to photocatalysis and solar energy conversion.